The separation of metal ions present as contaminants in water is complicated by the presence of organic substances. The two most popular technologies for the removal of metal ions are solvent extraction and ion exchange. Solvent extraction offers the advantage of fast kinetics, high capacities and selectivity (Ritcey, G. M Separation Science and Technology, 18, 1617, 1983). But solvent extraction cannot be used for dilute solutions. Ion-exchange resins contain functional groups capable of complexing with the metal ions. The resins can be regenerated and reused. However the disadvantages of these resins are slow reaction kinetics and poor selectivity which also deteriorates in the presence of other competing metal ions (Beauvais, R. A., Alexandros, S. D. Reactive and Functional Polymers, 36, 113, 1998).
The application of molecular imprinting for the selective removal of a metal ion was first reported by Nishide (Nishide, H., Deguchi, J., Tsuchida, E. J. Polym. Sci. Chem. Ed 15, 3023, 1977) Different approaches have been reported so far for metal ion imprinted resins. In the first approach linear polymer carrying metal ion binding groups or ligands are synthesized. These polymers are then treated with the metal ion to be imprinted and crosslinked with the help of a bifunctional reagent. MIPs selective for metal ions like copper/cobalt/nickel were reported (Effendiev, A. A., Kabanov, V. A., Pure and Applied Chem. 54, 2077, 1982.). The copper imprinted polymer so synthesized showed selectivity for copper in the presence of nickel and cobalt ions. In another approach (Kuchen, W. Schram, J. Angew. Chem. Int. Ed. Engl. 27, 1695, 1988) isolated a copper complex of acrylic acid and polymerized it with ethylene glycol dimethacrylate. The imprinted resins exhibited an increased affinity for copper in presence of other metal ions like Cd, Zn. Since the resin has to be used in continuous circulation mode, the rebinding kinetics should be fast. Surface imprinted polymers would have a better advantage over conventional imprinted polymers. This was investigated by Dhal et al (1995) by grafting copper (II) complex of N(4-vinylbenzyl imino) diacetic acid on the surface of microporous poly(trimethylol propane trimethacrylate) support. These polymers exhibited selective rebinding of Cu2+ and faster binding kinetics. Besides these, amino acid modified crosslinked biopolymers like glucan etc have been used as chelating media for the removal of metal ions like copper, cobalt from brine solutions (Muzzarelli, R. A., Tanfani, F., Emanuelli, M., Bolognini, L. Biotech. Bioeng., 27, 1115, 1985). Though these polymers are superior in their capacity and kinetics of metal ion uptake they are susceptible to attack by microorganism and do not exhibit selectivity for a particular metal. Konishi et al (Konishi S., Saito, K, Furusaki, S. Ind. Eng. Chem. Res. 31, 2722, 1992) demonstrated the use of grafted hollow fiber membrane for efficient removal of cobalt ions. The use of NaY zeolite, erionite, and bentonite in the removal of radioactive cobalt from aq. solns. has been investigated (Carrera L. M., Gomez., S., Bosch, P., Bzilbulian, S. Zeolites, 13, 622, 1993).
Recently the inventors of the present invention have demonstrated the use of cobalt in bringing different functional group bearing monomers in proximity by complexation and subsequent polymerization of the complex on surface of porous microspheres (Karmalkar, R. N., Kulkarni, M. G., Mashelkar, R. A., Macromolecules, 1996, 26, 1366. Lele, B. S., Kulkarni, M. G., Mashelkar, R. A., React. Funct. Polym, 1999, 39, 37. Synthetic polymer exhibiting hydrolytic activity, its preparation and use for the conversion of esters and amides to the corresponding alcohol and amine. R. A Mashelkar, M. G. Kulkarni, R. N. Karmalkar., U.S. Pat. No. 5,870,578. July 1998).
The cooperative interactions of the functional groups during template rebinding were established. However, their selectivity for adsorption of cobalt was not investigated. In this patent we have described a process for the preparation of a cobalt imprinted polymer and its application for the selective removal of cobalt from aqueous solutions.